All known methods for recording musical compositions are based on recording of music on some storage medium in a recording room, and on their further reproduction (playback) in rooms, which are different from the recording room and have an acoustic environment varying in an unidentified manner. These methods ignore the influence of the room on the pattern of sounding emitted by a sound source, whereas sounding of any source is to some extent dictated by the spatial characteristics of environment, and always depends on the interaction between all factors of reflection, absorption, interference, dispersion of air acoustic vibrations, etc.; that is to say, since any sound in nature is “unique and inimitable”, its reproduction in the form of signal recorded on a digital (or any other) medium in case of reverse transduction to the acoustic form (through electroacoustic transducers) always results in loss of most of the content of primary sound because each transducer alone is a sound source and the signal that it emits is exposed to the environment of the audio room.
In some cases in order to get the desired pattern of sound, the signal is to be subjected to correction, including correction of AFC (amplitude-frequency characteristic), PFC (phase-frequency characteristic), time delays, spectrum modifications, etc. which taken together endow the sounding with the tentative averaged characteristics preset in digital signal processor. That is to say, based on the analysis of acoustic properties of a room by passing unified test signals through the system, which involves “processor (signal synthesizer)—electroacoustic transducer—acoustic environment (room)—acoustoelectric transducer (microphone)—processor (signal response analyzer)” the audio signal is corrected so that to make the sound pattern correspond to one of the proposed types (preset in the signal processor) or to any other type (not specified). Such methods are not able to re-create the sound pattern of original performance of musical programme faithfully because the specific difference in acoustic characteristics between the recording room (primary environment) and reproduction room (secondary environment) is unknown, and there is a record of primary performance only (musical instruments and vocalists may serve as the sound source, while the room may be represented by a studio, concert-hall, opera house, restaurant, pedestrian underpass, etc.) and uncertain acoustic environment of the record reproduction having its own specific nature and features (the sound source is some digital audio system, and unknown room where the record is reproduced).
A related art application RU200411324 relates to the method for reproduction of audio characteristics of a particular environment which implies that at least a part of sound-reflecting and sound-absorbing surfaces in the environment is represented as a virtual “twin” of the environment through their recording by parameterized filters. Each surface has a bank of parameterized filters created with consideration for its sound-reflecting and sound-absorbing characteristics, as well as for relative audio position of surfaces. The banks of parameterized filters are saved and restored when reproducing the audio characteristics of the environment so that to create the virtual twin of the environment. All sound-reflecting and sound-absorbing surfaces of the environment are represented as the virtual twin of the environment. Active sound-reflecting and sound-absorbing surfaces of the environment are represented as the virtual twin of the environment.
First, the above method offers a total or partial representation of the acoustic space as a mathematical model, namely, a parametric description of all or any of surfaces involved in the formation of room acoustics. The new method proposes that the space should be represented by a description of variations of test signals which result from the testing of recording room with the use of a reference signal other than by description of the surfaces, as such. In other words, the new method gives a complex result: an initial response (in an explicit or in a parametric form, herein also called a ‘primary response’), which can be represented in any form (as functions, parameters or digital sound signals). Second, the reproduction of audio characteristics of the environment (e.g., a musical room) involves “restoration of banks of parameterized filters so that to ensure the creation of virtual twin of the environment,” which means that the parameterized filters being used to describe the surfaces of the environment are restored and apparently repeated during the reproduction. However, filters having parameters of the primary environment cannot be just applied to the audio signal being reproduced in the audio reproduction room, because the audio reproduction room has unknown parameters, which will have an additional effect upon the reproduction quality (performance of the known filter parameters of one room will be necessarily supplemented with the effect of unknown parameters of another room). That is, the room wherein the primary room's audio characteristics are to be reproduced (re-established) also must be tested with the reference signal by the same method used to get the primary response so that to determine the influence of the audio reproduction room on the reference signal.
The results of testing are to be represented as secondary response signals. Further comparison between the secondary response and primary response (i.e. the results of testing of two different rooms by the same signal) makes it possible to define new banks of parameterized filters for the musical signal in order to re-create the desired acoustic conditions (environment) existed during the performance and recording of music in the recording room by making the appropriate calculations. Such new filters can be applied to restore (re-establish) the audio characteristics of the primary room in a different one. In reality, none of the users who got a musical record for reproduction will do that on his own since he doesn't have appropriate equipment.
A prior art application RU2000112549 relates to the method for processing of virtual acoustic environment incorporating surfaces of a transmitter and receiver. The method is distinctive in that the surfaces incorporated in the virtual acoustic environment are described by filters which effect on the audio signal depends on parameters relevant to each filter, and are transmitted from the transmitter to the receiver. The parameters relevant to each filter are coefficients that characterize acoustical reflection and/or absorption and/or transmission of the surfaces. The above method has the drawbacks identical to those of the previous one, that is, it offers a description of space pattern by means of parameterized filters.
Besides, the method involves the steps when the transmitter creates some virtual acoustical environment having the surfaces which are represented by filters which effect on the audio signal depends on the parameters relating to each filter; the transmitter transfers the parameters to the receiver; in order to re-create the virtual acoustical environment the receiver is to make bank of filters which effect the audio signal depending upon the parameters of each filter, and to set up parameters based on the information transferred by the transmitter.
According to the aforementioned method, the transmitter creates surface-representing filters and transfers their parameters to the receiver; the receiver creates filters which parameters depend on the parameters received from the transmitter; that is, the receiver, as in the previous method, ignores the influence of the parameters of its acoustical environment, while this influence must necessarily be taken into account, otherwise proper correction of musical signal is impossible.